1. Field of the Invention
This invention relates to an alloy target which is suitable for use in the manufacture of a magneto-optical recording medium by sputtering.
2. Description of the Prior Art
A magneto-optical memory has been drawing a great deal of attention as it facilitates the erasure and re-recording of information. Single-crystal materials such as garnets, polycrystalline materials such as MnBi and PtCo, or amorphous materials such as alloys of rare earth elements and transition metals are usually employed for manufacturing a magneto-optical memory.
The use of an amorphous alloy comprising a rare earth element or elements and a transition metal or metals, such as Tb--Fe--Co or Gd--Tb--Fe, provides a variety of advantages. For example, it enables the manufacture of a magneto-optical memory which requires only a small amount of energy for recording information, one which is free from any grain boundary noise, or one having a relatively large size. A film of such an amorphous alloy is often formed by sputtering, i.e., by causing ions to collide with a target to form a film of a substrate positioned near it. The target usually comprises (1) a composite material prepared by attaching chips of a rare earth element to a sheet of, e.g., iron, or embedding them therein, (2) an alloy prepared by melting a rare earth element and a transition metal by, e.g., arc discharge, or (3) a sintered compact prepared by mixing an alloy powder which has been obtained by crushing a lump of an alloy formed by melting a rare earth element and a transition metal, with a transition metal powder, and sintering their mixture by powder metallurgy, as described in Japanese Laid-Open Patent Specification No. 230903/1985.
A good target material is one which satisfies the following requirements:
(a) High toughness; PA1 (b) A structure which is sufficiently dense to ensure the stability of sputtering to form a film; PA1 (c) A composition which is sufficiently uniform to ensure the formation of a film of uniform composition; PA1 (d) An oxygen content which is sufficiently low to ensure the formation of a film having good magneto-optical properties; and PA1 (e) A low cost.
None of the known materials as hereinabove described, however, satisfies all of the requirements. More specifically, the material as set forth at (1) above fails to satisfy the requirements (c) and (e), the material as set forth at (2) fails to satisfy the requirements (a), (d) and (e), and the material as set forth at (3) fails to satisfy the requirements (b), (d) and (e).